Heat transfer apparatus with osmotic pumping

ABSTRACT

An apparatus for transferring thermal energy from a heat source to a heat sink having a closed space containing a saline solution and an evaporator wherein the heat input evaporates the liquid so that a water vapor moves toward a condenser where heat is rejected to return the water vapor to the liquid phase. The closed space containing the saline solution extends to the region of the condenser and has a water permeable membrane positioned adjacent the condenser. The water is returned to the evaporator by osmotic pumping.

United States Patent I [451v July 18, 1972 Midolo [54] HEAT TRANSFERAPPARATUS WITH OSMOTIC PUMPING [72] inventor: Lawrence L. Midolo,Centerville, Ohio [73] Assignee: The United States of America asrepresented by the Secretary of the Air Force [22] Filed: Sept. 10, 1970[21] Appl.No.: 70,977

[52] U.S. Cl... ..l65/l05 [5 1] Int. Cl. ..F28d 15/00 [58] Field ofSearch 165/105 [56] References Cited UNITED STATES PATENTS 3,561,5252/1971 Baer ..l65/l05 Primary Examiner-Albert W. Davis, Jr. AttomeyHarryA. Herbert, Jr. and Richard J. Killoren ABSTRACT An apparatus fortransferring thermal energy from a heat source to a heat sink having aclosed space containing, a saline solution and an evaporator wherein theheat input evaporates the liquid so that a water vapor moves toward acondenser where heat is rejected to return the water vapor to the liquidphase. The closed space containing the saline solution extends to theregion of the condenser and has a water permeable membrane positionedadjacent the condenser. The water is returned to the evaporator byosmotic pumping.

9 l0 Clalns, 7 Drawing Figures Patented July 18, 1972 3,677,337

2 Sheets-Sheet 2 Fig-E INVENTOR. zflwenvca 4. 31/0 0 BY flrrol? y HEATTRANSFER APPARATUS WITH OSMOTIC PUMPING BACKGROUND OF THE INVENTIONVarious techniques have been used for transferring thermal energy from aheat source to a heat sink. These include systems that rely on thermalconduction, forced convection, and systems which depend upon evaporationand condensation of a heat exchange fluid. The systems which depend uponevaporation and condensation of a heat exchange fluid overcome some ofthe shortcomings of other heat exchange systems. However, the systemswhich depend upon evaporation and condensation of a heat exchange fluiddepend upon gravity or capillary pumping to return the cooling liquid tothe heat source. These systems suffer from orientational problems andare not suitable in a high gravitational field or in an aircraft flightdynamic environment wherein the pumping force of such systems isexceeded by the gravitational force or the flight dynamic forces.

BRIEF SUMMARY OF THE INVENTION According to this invention use is madeof osmotic pressure to transport the working fluid from the heat sink tothe heat source in a system that depends upon the evaporation andcondensation of a heat transfer fluid as the heat transfer medium. Aheat transfer system using osmotic pumping with zero gravity, equaldiameter heat pipes and the same basic configuration as used in acapillary pumping system will provide approximately 10 times the heattransfer capacity. Also the osmotic pumping will operate at highergravity levels where the capillary pumping will cease to operate.

IN THE DRAWING FIG. 1 is a schematic illustration of a heat transfersystem according to the invention.

FIG. 2 is an enlarged partially cut away sectional view of the condenserand permeable membrane for the device of FIG. 1.

FIG. 3 is an enlarged partially cut away sectional view of a modifiedcondenser section for the device of FIG. 1

FIG. 4 is an enlarged partially cut away sectional view of a furtherembodiment of the invention.

FIG. 5 is an enlarged partially cut away sectional view of anotherembodiment of the invention.

FIG. 6 is a schematic illustration of a heat transfer system of anotherembodiment of the invention.

FIG. 7 is an enlarged partially cut away sectional view of the heatinput section of the device of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION With reference to FIG. 1 of thedrawing reference 10 shows a heat transfer system having a heat inputsection 12 and a condenser section 14. A double wall container 16 has aspace 17 between the inner wall 18 and the outer wall 19 to hold asaline solution which is preferably a saturated solution. The doublewall container may be made of a material such as stainless steel. Awater permeable membrane 20 of a material such a cellulose acetate,polyvinyl chloride or polyvinyl alcohol, covers an opening at the lowerend of walls 18 and 19. The membrane may be secured to walls 18 and 19in conventional manner, for example with an adhesive. A metal screen, asupport of sintered bronze or other known type of support, not shown,may be used to provide support for membrane 20, if needed. The salinesolution empties into an evaporation chamber 22. The heat input tochamber 22 causes water to evaporate from the saline solution and leavechamber 22 through aperture 24. Very little salt leaves with the watervapor so that the device can operate for a considerable time beforecleaning is needed.

The vapor passing through aperture 24 is condensed at condenser surface25 of condenser plate 26. The condenser plate 26 may be made of amaterial such as aluminum or copper. The condensed water vapor collectsin space 27 between condenser surface 25 and the membrane 20 where it isreturned to space 17 by osmotic diffusion pumping. When the ambienttemperature near condenser plate 26 is sufficiently low, no special heatsink is required. However, when needed cooling coils or other coolingmeans, not shown, may be provided adjacent condenser plater 26.

A metal mesh wick 30, of a material such as aluminum or copper may beprovided adjacent condenser surface 25 and membrane 20, as shown in FIG.3. Other configurations for the condenser section and permeable membranethan thus far described may also be used, if desired. For example, thecondenser and permeable section may be as shown in FIG. 4. In thisdevice the wall 19' extends across a portion of the bottom of channelsection 32. The membrane 20' is then positioned as a parallel extensionof wall I8 and is secured to wall 18' and the extension of wall 19.

Since the water flux through the membrane is a function of the area ofthe membrane, the water flux can be increased by increasing the area ofthe membrane as shown in FIG. 5. In this device walls 18" and 19" havecurved extensions 33 perpendicular to the walls. The membrane 20" has asinuous configuration and is secured to projections 33 on walls 18" and19". Other configurations can also be used to increase the surface areaof the water permeable membrane.

With the device thus far described, as can be seen from FIG. 1, tiltingor inverting the apparatus would tend to cause saline solution to passthrough aperture 24. Thus, this device is suitable only when theapparatus is substantially stationary 'or where an artificial gravitywould keep the saline solution in place. In some flight dynamicenvironments some means must be provided to keep the saline solutionfrom entering the chamber adjacent surface 25. The device of FIGS. 6 and7 can be used to overcome these problems. In this device a wick 35 ispositioned adjacent end wall 37 and extends into the space 38 betweenwalls 40 and 41. The wall 40 extends over to contact the wick 35adjacent wall 41. Other apparatus than that shown may be used forcontaining the saline solution within chamber 37.

While metal mesh wicks have been described as the wick material, otherwick materials can be used, for example, glass beads, avril rayon clothor felt material.

The solutes used may be any water soluble material which will not passthrough or attack the particular membrane used. Examples of solutematerials that can be used are the water soluble clorides such as NaCl,I(Cl and Cacl the water soluble chlorates such as K,co,, cs,co, CsH CONa CO and the water soluble borates, such as Na,B,O -l0H,O. Also somesugars can be usedwith certain membranes.

While saline solution andwater have been described as the workingagents, other materials may also be used, for example sugar could besubstituted for salt in some applications.

There is thus provided an improved apparatus for transporting thermalenergy from a heat source to a heat sink.

I claim:

1. Apparatus for transferring thermal energy from a heat source to aheat sink, comprising: a closed container having a first portion adaptedto be positioned adjacent the heat source and a second portion adaptedto be positioned adjacent the heat sink; means for dividing said closedcontainer into a first compartment and a second compartment, a liquidsolution of predetermined concentration in said first compartment,means, within said container adjacent the first portion, for permittingthe flow of solvent vapor evaporated by said heat source to flow intothe second compartment; means extending into the second compartmentadjacent the second portion of said container for providing a condensingsurface for the solvent vapor; and a membrane, permeable only to thesolvent, of the solution, positioned adjacent said condensing means andlocated between the first compartment and the second compartment wherebythe condensed solvent is pumped toward the first portion of said closedcontainer by osmotic diffusion pumping.

2. The device as recited in claim 1 wherein the solvent is water and thesolute in the solution is a water soluable salt selected from the groupNa Cl, K Cl, CaCl,, K,CO Cs,CO,,-

Csl-l C0,, Na,CO;,, Na B H 0.

3. The device as recited in claim 2 wherein said first and secondcompartments are concentrically positioned compartments separated by acylindrical wall member extending to a position adjacent the condensingmeans; said permeable membrane being annular in shape and closing thespace between the wall of the closed container and said wall memberpositioned adjacent the condensing means.

4. The device as recited in-claim 3 including a wicking materialpositioned in said second compartment at the first portion of saidcontainer'and having a portion extending into the second compartment;said cylindrical wall having means for closing the end of said firstcompartment adjacent the heat source except for the portion where thewicking material extends into the first compartment.

5. The device as recited in claim 3 wherein wick material is positionedover the condensing means and contacts the permeable membrane.

6. The device as recited in claim 3 including an annular channelsurrounding the condensing means with the condensing means and saidchannel forming one endwall of the container; the side wall of saidcontainer and said cylindrical wall member extending into said annularchannel and forming an opening adjacent the condensing means; saidpermeable membrane forming a closure for said opening to thereby providean osmotic barrier permeable only to said solvent.

7. The device as recited in claim 6 including means for providing agreater length of permeable membrane than the circumferential length ofsaid cylinder wall member.

8. The device as recited in claim 7 wherein the means for providing agreater length of permeable membrane includes means projecting from theside wall and the cylindrical wall member toward said condensing means.for forming substantially sinusoidal shaped edges; said permeablemembrane having a substantially sinusoidal shape conforming to thesubstantially sinusoidal shaped edges.

9. The device as recited in claim 7 wherein wick material is positionedover the condensing means and connects the permeable membrane.

10. The device as recited in claim 2 wherein the solute is Na Cl.

1. Apparatus for transferring thermal energy from a heat source to aheat sink, comprising: a closed container having a first portion adaptedto be positioned adjacent the heat source and a second portion adaptedto be positioned adjacent the heat sink; means for dividing said closedcontainer into a first compartment and a second compartment, a liquidsolution of predetermined concentration in said first compartment,means, within said container adjacent the first portion, for permittingthe flow of solvent vapor evaporated by said heat source to flow intothe second compartment; means extending into the second compartmentadjacent the second portion of said container for providing a condensingsurface for the solvent vapor; and a membrane, permeable only to thesolvent, of the solution, positioned adjacent said condensing means andlocated between the first compartment and the second compartment wherebythe condensed solvent is pumped toward the first portion of said closedcontainer by osmotic diffusion pumping.
 2. The device as recited inclaim 1 wherein the solvent is water and the solute in the solution is awater soluable salt selected from the group Na Cl, K Cl, CaCl2, K2CO3,Cs2CO3, CsH CO3, Na2CO3, Na2 B4O7 .10 H2O.
 3. The device as recited inclaim 2 wherein said first and second compartments are concentricallypositioned compartments separated by a cylindrical wall member extendingto a position adjacent the condensing means; said permeable membranebeing annular in shape and closing the space between the wall of theclosed container and said wall member positioned adjacent the condensingmeans.
 4. The device as recited in claim 3 including a wicking materialpositioned in said second compartment at the first portion of saidcontainer and having a portion extending into the second compartment;said cylindrical wall having means for closing the end of said firstcompartment adjacent the heat source except for the portion where thewicking material extends into the first compartment.
 5. The device asrecited in claim 3 wherein wick material is positioned over thecondensing means and contacts the permeable membrane.
 6. The device asrecited in claim 3 including an annular channel surrounding thecondensing means with the condensing means and said channel forming oneend wall of the container; the side wall of said container and saidcylindrical wall member extending into said annular channel and formingan opening adjacent the condensing means; said permeable membraneforming a closure for said opening to thereby provide an osmotic barrierpermeable only to said solvent.
 7. The device as recited in claim 6including means for providing a greater length of permeable membranethan the circumferential length of said cylinder wall member.
 8. Thedevice as recited in claim 7 wherein the means for providing a greaterlength of permeable membrane includes means projecting from the sidewall and the cylindrical wall member toward said condensing means, forforming substantially sinusoidal shaped edges; said permeable membranehaving a substantially sinusoidal shape conforming to the substantiallysinusoidal shaped edges.
 9. The device as recited in claim 7 whereinwick material is positioned over the condensing means and connects thepermeable membrane.
 10. The device as recited in claim 2 wherein thesolute is Na Cl.